CSFB optimization Radio LTE optimization and LTE SON & Site Integration process workshop Milan , 26-27 May 2015
C2 – Vodafone Restricted
Agenda
1. CSFB principle 2. Performance key factors 3. Call phases – –
4G leaving and RAT camping Legacy RAT registration
4. Case study: MOC 4G to MTC 3G Insert Confidentiality Level in slide footer
C2 – Vodafone Restricted
CSFB principle Voice evolution in three steps:
From Single radio to Convergence Source: Qualcomm
• Longer call setup time (+2/3 sec with 3G as landing RAT) • Additional 3,5s in case of CSFB to 2G • Worse Call Setup Success Rate (1%) C2 – Vodafone Restricted
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Performance ¦ key factors Overall call setup time performance strongly depends on the scenario considered and radio/core implementation - Call scenarios: Mobile-to-Mobile or Mobile to Fixed/ISDN benchmark tests might have very different performance in terms of call setup time and accessibility. - Landing radio access technology: preferred technology and radio fallback strategy are crucial for determining the average call setup time. - Core Architecture: Overlay MSS or pooling Core CS architecture could significantly impact call setup time performance. - NAS procedures: frequency of security procedures (Authentication, Identity,… ) executed during call setup might introduce high variance in the overall setup time.
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Common phases for MOC and MTC: 1. 2. 3. 4. 5.
4G leaving Legacy RAT camping Legacy RAT registration Setup Alert
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Mobile Terminated call
Identification of call setup phases and relevant trigger points
Mobile Originated call
Call phases ¦ MOC and MTC
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4G leaving and RAT camping /1
Accessibility
Call Setup Time
Operational effort
Commercial Drivers
RRC Release with Redirect 1. Basic without target RAN System Information (SI) : Easy implementation and fast deployement, longer call set-up time because SI needs to be fetched by the UE in the target RAN
2. Enhanced CSFB: i. Deferred Measurement Control Reading (WCDMA) RACH access is performed after reading SIB 1,3,5 and 7 only (SIB11 containing neighbour info are sent in the Measurement control message) . Valid for >Rel7 UE . Gain: hundred ms. SIB caching implementation in the device could prevent the usage of deferred SIB.
ii.
SI exchange based on 3GPP RIM procedures (GSM and WCDMA) System Info are provided via LTE redirection message (via core network ). Gain : 0,8s in 3G and 2.5 in 2G
PSHO (Packet Switched Handover) 3G cell measurement are performed and if a 3G suitable cell is found, the PS handover to UE is sent (improve call setup time ~0,8s and accessibilty). C2 – Vodafone restricted
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4G leaving and RAT camping /2 Landing technology strategy is crucial for guaranteeing a good level of accessibility and call setup time HIGH Start Band
LOW LANDING TECNOLOGY / BANDS
L1800
U2100
U900
G1800
G900
L2600
U2100
U900
G1800
G900
L800
U900
G900
other
• Strategy is based on the footprint of the different ‘coverage’ layers taking into account the propagation of each layer. • In case of non-contiguous/homogeneous layer, hybrid solution with different CSFB implementation could be adopted. 7 C2 – Vodafone restricted
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4G leaving and RAT camping /3 In case of Mobile terminated call, paging timer and repetition scheme influence call setup time CS paging repetition timer (from UE perspective) has to be carefully set. Depending on the total number of repetition available on MSC, paging repetition on both MME and eNodeB could be exploited.
Fine tuning of DRX cycle and paging occasion settings for saving time in order of tens milliseconds
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Legacy RAT registration Not-pooled (GMSC) architecture
Pooled MSC architecture
In a pure not-pooled MSC architecture , fallback always occurs in MSC that are different from the GMSC and Location Update procedure is needed (inter-MSC scenario with HLR involved) during call setup.
In a pure not-pooled MSC architecture, LAU is not performed during the call setup Real Combined TA/LA Direct SG interface (MME-MSC)
Each legacy MSC has dedicated “virtual” LAC. MME is configured with a mapping between TACs and “virtual” LAC of the MSC. in legacy MSCs: each “virtual” LAC points to overlay MSC
Fast implementation from operational perspective but longer setup time in CSFB MOC and MTC and lower reachability in MTC due to a frequent Loc. Upd. Call setup time improvement
Avoidong Location Update, call setup is shorter (500ms) but potential short period of unreachability after the call.
CSMT FLAG Essential to avoid the paging lost after LAU and reallocate signalling resources on the A-interface. LA Update & call setup performed in one single radio connection setup Mobile Terminating Roaming Forwarding (MTRF) Avoid release the call leg to the G-MSC, reducing signalling flow and MTInsert procedure Confidentiality Level in slide footer C2 – Vodafone restricted
Increased complexity in radio planning and MME TAC/LAC mapping 9
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Case study: MOC 4G to MTC 3G ¦ Message flow
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Case study: MOC 4G to MTC 3G ¦ Typical performance
All Operators with: • RRC Release with Redirect • Preferred landing technology: UMTS • Pooled MSC architecture C2 – Vodafone restricted
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Case study: MOC 4G to MTC 3G ¦ Time distribution 1
side1(from 4G RRC conn release to 3G RRCconn req) 100,00% 90,00% 80,00% 70,00% 60,00% 50,00% 40,00% 30,00% 20,00% 10,00% 0,00%
0,23 0,43 0,52 0,61 0,7 0,79 0,88 0,97 1,06 1,15 1,24 1,34 1,43 1,52 1,61 1,7 1,79 1,88 1,97 2,06 2,16 2,27 2,36 2,48 2,58 2,69 2,79 2,91 3,02 3,25 3,95 4,54 5,31
Operator A OperatorEEB OperatorTelefonica C Three Vodafone Operator D
Operator C: • More session with UMTS landing technology • Deferred SIB
Duration [s] C2 – Vodafone restricted
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Case study: MOC 4G to MTC 3G ¦ Time distribution 2
side1 (from call proceeding to alerting)
100,00% 90,00% 80,00% 70,00% 60,00%
EE A Operator Telefonica Operator B Three Operator C Vodafone Operator D
50,00% 40,00% 30,00% 20,00% 10,00%
Operator C: • No Authentication/Cyphering procedures • Early RAB assigment on Terminated side
0,05 0,52 1,17 1,76 2,04 2,26 2,48 2,7 2,92 3,14 3,36 3,58 3,8 4,02 4,24 4,46 4,68 4,9 5,12 5,34 5,56 5,78 6 6,22 6,44 6,69 6,95 7,27 7,6 8,01 8,42 8,76 9,37 9,93
0,00%
Duration [s] C2 – Vodafone restricted
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